Add microsoft oauth2 providers (#16544)

* Clean up oauth2 providers

Signed-off-by: Andrew Thornton <art27@cantab.net>

* Add AzureAD, AzureADv2, MicrosoftOnline OAuth2 providers

Signed-off-by: Andrew Thornton <art27@cantab.net>

* Apply suggestions from code review

* remove unused Scopes

Signed-off-by: Andrew Thornton <art27@cantab.net>

Co-authored-by: techknowlogick <techknowlogick@gitea.io>

services/auth/source/oauth2/providers_openid.go

@@ -0,0 +1,52 @@
+// Copyright 2021 The Gitea Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package oauth2
+
+import (
+	"code.gitea.io/gitea/modules/log"
+	"code.gitea.io/gitea/modules/setting"
+
+	"github.com/markbates/goth"
+	"github.com/markbates/goth/providers/openidConnect"
+)
+
+// OpenIDProvider is a GothProvider for OpenID
+type OpenIDProvider struct {
+}
+
+// Name provides the technical name for this provider
+func (o *OpenIDProvider) Name() string {
+	return "openidconnect"
+}
+
+// DisplayName returns the friendly name for this provider
+func (o *OpenIDProvider) DisplayName() string {
+	return "OpenID Connect"
+}
+
+// Image returns an image path for this provider
+func (o *OpenIDProvider) Image() string {
+	return "/assets/img/auth/openid_connect.svg"
+}
+
+// CreateGothProvider creates a GothProvider from this Provider
+func (o *OpenIDProvider) CreateGothProvider(providerName, callbackURL string, source *Source) (goth.Provider, error) {
+	provider, err := openidConnect.New(source.ClientID, source.ClientSecret, callbackURL, source.OpenIDConnectAutoDiscoveryURL, setting.OAuth2Client.OpenIDConnectScopes...)
+	if err != nil {
+		log.Warn("Failed to create OpenID Connect Provider with name '%s' with url '%s': %v", providerName, source.OpenIDConnectAutoDiscoveryURL, err)
+	}
+	return provider, err
+}
+
+// CustomURLSettings returns the custom url settings for this provider
+func (o *OpenIDProvider) CustomURLSettings() *CustomURLSettings {
+	return nil
+}
+
+var _ (GothProvider) = &OpenIDProvider{}
+
+func init() {
+	RegisterGothProvider(&OpenIDProvider{})
+}